When a vehicle is traveling on a cant road having an inclination in its width direction, or when the vehicle is traveling in a crosswind, the vehicle drifts to the lower side in the inclination direction on the cant road under the influence of gravity, or drifts to the leeward side in the crosswind under the influence of wind power. Such a behavior is called a one-side pull of a vehicle. In order to keep driving the vehicle straight under cruise control against the one-side pull behavior of the vehicle, a driver needs to keep steering a steering wheel to the upper side in the inclination direction or to the windward side. To put it differently, in order to maintain straight travel of the vehicle in a situation where the one-side pull behavior of the vehicle occurs, the driver needs to continually provide a steering force in a direction opposite the direction the vehicle drifts (the direction of the one-side pull).
For example, Japanese Patent Application Publication No. 2015-37932 discloses a vehicle steering device having: an electric motor; a steering angle sensor; a steering torque sensor; and an EPS_ECU configured to control, when a vehicle is traveling straight, driving power of the electric motor based on vehicle information including a steering torque and a steering angle, and thereby perform control to apply an assist torque on a steering system. In the vehicle steering device according to Japanese Patent Application Publication No. 2015-37932, the EPS_ECU includes: an integrating unit configured to calculate an integrated torque value obtained by integrating the steering torque; and a wheel-alignment support controlling unit configured to perform anti-one-side pull control based on the integrated torque value when the integrated torque value is equal to or above a threshold.
According to the vehicle steering device of Japanese Patent Application Publication No. 2015-37932, it is possible to provide steering comfort to a driver even in a situation where the one-side pull behavior of the vehicle occurs during traveling on a cant road or during traveling in a crosswind, by executing anti-one-side pull control for suppressing the one-side pull behavior of the vehicle.